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Asthma: Use a peak flow meter to gain control
Using a peak flow meter is a simple but important part of your daily asthma management plan. Here's help determining your personal best and understanding your peak flow zones.
By Mayo Clinic staffA peak flow meter is a simple, easy-to-use device that measures how well your lungs are working. By measuring how efficiently you can breathe air out of your lungs, peak flow readings can help you identify worsening asthma so that you can adjust your treatment. Along with carefully watching your symptoms, you can use peak flow readings to help determine what steps you need to take to keep your asthma under control.
With time on your side, you can adjust your asthma medication and take other steps to help prevent an attack. In some cases, you may even notice changes in your peak flow before you have any signs or symptoms. A peak flow meter can be especially important if you have a hard time judging the severity of your symptoms, you have had severe asthma attacks, or you have moderate or severe asthma.
How a peak flow meter helps you
A peak flow meter allows you to accurately measure day-to-day variations in your breathing. When your asthma is under control, your airways are open and you can force more air into the peak flow meter. But when your airways are inflamed and constricted, you can't blow as hard into the meter — making your peak flow rate lower.
These readings will help you and your doctor:
- Determine the severity of your asthma
- Evaluate the effectiveness of your current treatment
- Determine when to add or stop certain medications
- Recognize an asthma attack before signs or symptoms appear
- Decide when to seek emergency care
Determining your personal best
Your "personal best" peak flow rate is the highest peak flow rate you can reach over a two- to three-week period when you feel good and have no asthma symptoms. This flow rate serves as a benchmark in your daily self-management plan. Because everyone's asthma is different, your personal best will be unique to you.
Your doctor will help you determine your personal best. Typically, you'll take readings once or twice a day for two weeks when you're not having symptoms. The highest consistent reading during the trial period is your personal best.
Organizing your peak flow zones
Your doctor will use your personal best peak flow rate to set your peak flow zones. Each zone is determined by your peak flow rate and symptoms. The color code for each zone reflects progressively more severe symptoms:
Green zone = stable
- Your peak flow rates are 80 percent to 100 percent of your personal best, an indication that your asthma is under control.
- You probably have no asthma signs or symptoms.
- Take your preventive medications as usual.
- If you consistently stay within the green zone, your doctor may recommend reducing your asthma medication.
Yellow zone = caution
- Your peak flow rates are 50 percent to 80 percent of your personal best, an indication that your asthma is getting worse.
- You may have signs and symptoms such as coughing, wheezing or chest tightness — but your peak flow rates may decrease before symptoms appear.
- You may need to increase or change your asthma medication.
Red zone = danger
- Your peak flow rates are less than 50 percent of your personal best, an indication of a medical emergency.
- You may have severe coughing, wheezing and shortness of breath. Stop whatever you're doing and use a bronchodilator or other medication to open your airways.
- Your asthma action plan will help you decide whether to call your doctor, take an oral corticosteroid or seek emergency care.
If your flow readings fall too far below your personal best — into the yellow or red zone — you'll need to take action to prevent or minimize an asthma attack.
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